1. Field of the Invention
This invention relates in general to a screen grid electron tube and particularly to a construction for cooling such tube.
2. Description of the Prior Art
Radio frequency currents cause additional losses in the operation of electron tubes at high frequency. This is particularly true for transmitter tubes which are operated with high AC anode voltages. The radio frequency currents produced by the AC anode voltage produce losses in the screen anode space on the leads and on the electrodes that must be provided for special cooling.
In radio frequency tube power amplifiers having frequencies from 100 MHz through 1000 MHz, in other words, in the VHF or the UHF range, particularly in the IV/V range, the cooling of the tube terminals presents a considerable problem. When operating at high frequencies, tubes must be short and compact as possible. However, this makes it more and more difficult to eliminate the heat generated.
Particularly, in high powered tubes for transmitters in the IV/V UHF range, the dimensions such as the length of the system and the length of the leads are extremely short due to the electrical wave length. Also, the thermal conductivity of the materials commonly used in tube technology is so high that heat elimination occurs by way of the terminals and these must therefore be appropriately cooled.
When using high powered tetrodes and power amplifiers such as cavity resonators, the cooling of the screen grid terminals requires special structural and cooling means.
Due to the radio frequency losses which occur at high frequencies, it is known to provide the screen grid terminal ring with a special air cooling guidance so that forced air cooling of this portion of the tube will occur. Two rows of rectangular openings are provided in this air cooling channel on both sides of the terminal surface to serve for the admission of air and the discharge of air. See for example, Senderoehren-Datenbuch 1980/1981, Page 147, Published by Siemens AG, Bereich Bauelemente, Munich, Federal Republic of Germany.
Transmitter tubes are also known wherein the screen grid terminal contains an integrated water cooling coil instead of an air cooling means and see, for example, NTG-Fachberichte, 1983, Pages 128-132, published by VDE-Verlag, Berlin, ISBN 3-8007-13217-7. Such cooling mechanism, however, makes it very difficult and time consuming to change a tube.